1. Technical Field of the Invention
This invention relates generally to medical diagnostic equipment and in particular to systems and methods for performing peripheral neuromuscular diagnosis with the stimulating device utilizing dry electrodes and having distance measurement capability.
2. Description of Related Art
In the medical field, nerve conduction tests or procedures are used to assess the functional status of the peripheral neuromuscular system. In the use of nerve conduction tests, when a nerve is stimulated electrically a reactions occurs somewhere along the nerve. The reaction of the nerve to the stimulation can be monitored with recording electrodes strategically placed on the patient. Direct recording of the reaction can be made along sensory or mixed sensory nerves, while indirect recording of the reaction from a muscle can be used for motor conduction tests. Both orthodromic conduction (an impulse traveling in the normal direction in a nerve fiber) and antidromic conduction (an impulse traveling in the opposite direction to that of normal in a nerve fiber) can be studied because nerve stimulus propagation occurs proximally to and distally to the point of stimulation. The time relationship between the stimulus and the response can be displayed, measured and recorded.
In the evaluation of motor nerves, motor responses are recorded over the target muscle being studied. Typically a recording electrode is placed over the motor point of the target muscle. A physical location on the patient is chosen along the nerve supplying the target muscle, at a select distance from the recording electrode, whereby when the electrostimulation is applied at the location, the response to the muscle can be recorded. Similarly, for sensory nerves, responses are recorded over the target nerve using surface electrodes. At the constant distance, distal or peak latency can be measured.
Some of the nerves tested require distal and proximal stimulation (e.g. wrist, elbow, and arm for median nerve). In such a case, the distance between the stimulation sites has to be measured to calculate conduction velocities. The conduction velocity of a nerve is calculated by measuring the distance between two stimulation sites and dividing by the difference in latency from the more proximal stimulus site and the latency of the distal stimulus site. Traditionally this distance is measured with nothing more than a measuring tape.
Traditionally, electrodes on the simulator that are used to stimulate the nerves are made with steel or gold plated steel and require the use of a messy electrode gels as a conductive medium between the electrodes and the skin.
Accordingly, there is a need for systems and methods for providing more accurate distance measurements without the use of messy electrode gels.